Polymers such as plastics, elastomers, and thermosets are used in large volumes in a wide range of applications such as walls, ceilings, furniture, floor coverings, fabrics, electronics, vehicles and electrical appliances. Because most polymers are flammable, fire safety is important in each of these applications. Generally, fire safety of polymers can be improved by incorporating flame retardants into the polymers. Flame retardants consist of compounds added to a material to improve the material's ability to withstand fire and heat or to resist combustion. Flame retardants can function in a variety of ways to reduce the risk of fire hazard. In one way, they can raise the ignition temperature. In the other ways, they can reduce the rate of burning, flame spread, or the generation of toxic gases and smoke. Phosphorus flame retardants can reduce the flammability of the polymer and reduce the generation of toxic gases and smoke.
There are many different kinds of flame retardants which include alumina trihydrate, magnesium hydroxide, halogenated compounds (e.g., chlorinated, fluorinated and brominated compounds), phosphorus compounds (e.g., phosphate esters), antimony oxide, melamine derivatives, and boric acid and other boron compounds. The worldwide sale of flame retardants was 2.35 billion pounds in 2003. It is predicted that the worldwide sale of flame retardants will increase to 2.82 billion pounds in 2008. Among all flame retardants, the two most common kinds are phosphorus flame retardants and halogenated flame retardants. Because of environmental and health concerns over halogenated flame retardants, many parts of Europe are considering bans on some specific halogenated flame retardants. Therefore, the trend is to restrain the use of the halogenated flame retardants and to migrate to other flame retardants such as phosphorus flame retardants. Some examples of phosphorus flame retardants currently in the market includes phosphate ester type flame retardants such as resorcinol bis(diphenyl phosphate) (RDP), bisphenol A bis(diphenyl phosphate), monomeric aromatic phosphate ester compounds (e.g., triphenyl phosphate and tricresyl phosphate) and the like. In general, resorcinol-based phosphate ester flame retardants such as RDP have some more desirable properties over the bisphenol A-based phosphate ester flame retardants because of the presence of meta-phenylene linkages in the former.
Some well known polymers, such as polycarbonates (PC) and polyphenylene oxide (PPO), have a wide range of industrial applications. In order to improve their impact strength properties, they are often blended with acrylonitrile-butadiene-styrene terpolymer (ABS) and high-impact polystyrene (HIPS). Since ABS and HIPS polymers are mainly hydrocarbon-based materials, they generally have a tendency to burn in the case of accidental fire. Though halogenated flame retardants are widely used with ABS and HIPS polymers, the phosphate ester type flame retardants are proven to be suitable for the PC/ABS and PPO/HIPS blends. It has been well known that resorcinol-based phosphate esters, such as RDP, are widely used in PC/ABS and PPO/HIPS blends as flame retardants. RDP can improve the melt flow properties and processability properties and enhance the char forming characteristics of the PC/ABS and PPO/HIPS blends. Similarly, other resorcinol-based phosphate ester flame retardants may also improve melt flow properties and processability properties of polymers while reducing the flammability of the polymers.
Generally, the flame retardants used in PC/ABS and PPO/HIPS blends are primarily aromatic phosphate esters based on resorcinol and bisphenol-A. Although these flame retardants can provide adequate flame retarding and other mechanical properties to PC/ABS and PPO/HIPS, there are always needs for improved flame retardants that can provide better melt flow and heat distortion performances than the resorcinol and bisphenol-A phosphate esters. Disclosed herein are new flame retardants that can meet the above-mentioned needs.